Heretofore, thermosetting adhesives have exhibited serious deficiencies in bond strength and flexibility when used with certain substrates such as Kapton (polyimide) film, polysulfone film, copper foil, or nickel foil. Phenolic adhesives and epoxy-phenolic adhesives suffer from brittleness and poor adhesion making them unsuitable for use on flexible substrates. These deficiencies, coupled with adhesive failure when electrical components are soldered, preclude their usage in many applications.
The Watanabe U.S. Pat. No. 3,932,689 shows a composition containing a cresol formaldehyde resin, a bisphenol based epoxy compound, an acrylonitrile-butadiene copolymer and several other components. Watanabe U.S. Pat. No. 4,323,659 discloses several compositions containing a bisphenol type epoxy resin, an acrylic copolymer, an imidazole accelerator and a brominated novolak. These compositions however, do not include an ethylene acrylic elastomer.
An object of the invention is to provide an adhesive with the flexibility and adhesion necessary for use with the above mentioned substrates.
A further object of the invention is to provide a thermosetting adhesive with improved bond strength and improved ability to withstand the various manufacturing conditions necessary to produce flexible circuitry (e.g., high temperatures, soldering, or etching).
A further object of this invention is to provide an adhesive that may be applied to film in solution form, or may be cast as a free-standing film itself to be used as an adhesive in laminated form.